1. Field of Invention
This invention relates to mechanical toys and educational devices, specifically to such toys and educational devices which are used for the simulation of earthquake ground shaking and potential damage or destruction of buildings and other structures.
2. Description of the Prior Art
Researchers in the world's major structural engineering laboratories frequently use large-scale shaker tables to perform earthquake studies and investigations. Shaker tables are also, but much less frequently, used by museum curators and science educators to provide an educational device for demonstrating concepts relating to earthquakes and for motivating students about earth science.
Originally, shaker tables were constructed as permanent installations in research laboratories. Such tables reproduce earthquake ground shaking motion for testing scale models of buildings and structures. Typically, tables in these laboratories are controlled by digital computers and driven by hydraulic actuators which enable researchers to meet the requirements of their earthquake studies. However, most non-researchers, including educators, cannot utilize these laboratory-based shaker tables because of their scarcity and their permanent nature. For example, the museum at the California Academy of Sciences possesses one of the very few such shaker tables outside of a research laboratory.
Thereafter, inventors created several types of shaker tables to reproduce or simulate earthquake ground motion without the necessity of permanent installations. The Oregon Museum of Science and Industry has developed shaker tables which can be relocated as part of a traveling earthquake exhibit; however, these tables require substantial set-up time and special facilities, including a continuous supply of compressed air for operation and motor vehicle accessibility for loading and transportation. Hence, these tables are not suitable for home or classroom use but are limited to use in assembly areas or special locations having the requisite facilities.
Environmental Volunteers of Palo Alto, Calif. developed a shaker table which can be relocated by one person and provides greater portability; however, the underlying mechanism of this table has an excessive number of machined parts which require custom manufacture. Thus, the table is cost prohibitive for home or educational use. This critical failing is borne out by the fact that previous manufacturers of this type of shaker table have scaled back or discontinued their production.
Several types of more economical shaker tables have been proposed; for example, Katharyn Ross, a researcher at the National Center for Earthquake Engineering Research, has put together a table using common materials. Her shaker table took the form of a cardboard table suspended by rubber bands from an exterior cardboard box frame. Ross tested it in a classroom setting albeit with limited effectiveness. Although portable and inexpensive to craft, said shaker table lacks the durability demanded for extended or repetitive use and the flexibility for varied modes of use. For instance, the table's rubber bands must be replaced often and the table's user cannot achieve a specific frequency of vibration which is essential to demonstrate the effects of earthquake motion on objects.
Shaker tables have been used for more than earthquake simulation. In addition, these tables were used to generate vibration for consolidating mixtures, such as concrete, and for aiding in sorting of materials, including food, medicine or grain products. However, in the mixing and sorting applications, the shaker table's intended use, internal mechanism, and vibrational characteristics do not coincide with those necessary for earthquake simulation.
The use of such shaker tables does not allow for users to mount the objects for subjection to earthquake-type shaking. Their shaking mechanisms are generally rotating cams which produce a motion of relatively high frequency. These vibrations are required to achieve reduction of inter-particulate surface friction in mixing and sorting. However, such vibrations are much higher in frequency than acceptable shaking motion for earthquake simulation.
All the shaker tables of the types heretofore mentioned suffer from several of the following known disadvantages:
(a) Tables of the type in present use generally are made of custom machined parts or components which result in tables which are prohibitively expensive for home or educational use. PA1 (b) Tables of the type in present use rely on methods of joining or assembling parts which do not lend themselves to mass manufacture. PA1 (c) Tables of the type in present use which have operating mechanisms using elastic rubber bands for table support generally are unreliable. PA1 (d) Tables of the type in present use made of typical construction materials like steel and concrete do not end themselves to economical modification or improvements. PA1 (e) Tables of the type in present use do not lend themselves to rapid setup and mounting of objects. PA1 (f) Tables of the type in present use are not sufficiently portable nor lightweight to permit carrying in a hand-held case. PA1 (g) Tables of the type in present use require external hydraulic, compressed air or electrical power sources which may not be readily available and which may represent a safety hazard in home or educational settings. PA1 (a) to provide a shaker table which minimizes the number of parts which require custom fabrication so that the table is inexpensive for home or educational use; PA1 (b) to provide a shaker table which uses joining or assembly methods which lend themselves to mass manufacture or end user assembly; PA1 (c) to provide a shaker table which is reliable in addition to being economical; PA1 (d) to provide a shaker table whose structure may be readily modified and improved or easily complemented by accessories; PA1 (e) to provide a shaker table which can be rapidly set up and onto which objects can be rapidly mounted; PA1 (f) to provide a shaker table which is portable and sufficiently lightweight to be carried in a hand-held case PA1 (g) to provide a shaker table that is powered by a self-contained power supply or hand operated to enable use in any setting.